Browsing by Author "Bshena, Osama"

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    Release of bacteriocins from nanofibers prepared with combinations of poly(D,L-lactide) (PDLLA) and poly(ethylene oxide) (PEO)
    (MDPI, 2011) Heunis, Tiaan; Bshena, Osama; Klumperman, Bert; Dicks, Leon Milner Theodore, 1961-
    Plantaricin 423, produced by Lactobacillus plantarum, and bacteriocin ST4SA produced by Enterococcus mundtii, were electrospun into nanofibers prepared from different combinations of poly(D,L-lactide) (PDLLA) and poly(ethylene oxide) (PEO) dissolved in N,N-dimethylformamide (DMF). Both peptides were released from the nanofibers with a high initial burst and retained 88% of their original antimicrobial activity at 37 °C. Nanofibers have the potential to serve as carrier matrix for bacteriocins and open a new field in developing controlled antimicrobial delivery systems for various applications.
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    Selected aspects of RAFT agents : the use of thiophene as an activating group in the RAFT mediated polymerization of styrene and the stereo-controlled polymerization of MMA via RAFT
    (Stellenbosch : Stellenbosch University, 2007-12) Bshena, Osama; Sanderson, R. D.; Weber, W.; Tonge, M.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: In this study six Reversible Addition-Fragmentation chain Transfer (RAFT) agents with different leaving groups and different activating moieties were prepared. Three are novel thiophene-based RAFT agents having a thiophene substituent as the activating moiety, namely: (2-thienyl thiocarbonyl)disulfide (BTD), 1-cyano-1-methylethyl 2-thiophene dithiocarboxylate (CPDT), and benzyl thiophene-2-dithiocarboxylate (BDTT). The other three are model RAFT agents bearing a phenyl group as the activating moiety, namely: bis(thiobenzoyl) disulfide (BBD), benzyl dithiobenzoate (BDTB), 2-cyano-2-yl dithiobenzoate (CPDB). These agents were characterized by Nuclear Magnetic Resonance spectroscopy (NMR), Fourier-Transform Infrared spectroscopy (FT-IR) and Ultraviolet - visible spectroscopy (UV/vis). These compounds were studied as RAFT agents, and used as mediators in the bulk polymerization of styrene, self-initiated thermally at 100 °C. The novel thiophene-based mediated systems were compared with the phenyl-based ones in terms of polymerization kinetics, molecular weight and polydispersity index (PDI). The polymerization results showed that the novel CPDT aiid !:!!)TT thiophene-based compounds were effective RAFT agents for the RAFT polymerization of styrene with the characteristics of "living"/controlled free radical polymerization. The BTD mediated system showed the poorest control, as the PDI progressively broadened with monomer to polymer conversion, and it had the lowest reaction rate. In general, the thiophene-based mediated systems had slower reaction rates (higher retardation) when compared to the analogous phenyl-based mediated systems. The RAFT technique was then used to synthesize stereo-controlled poly (methyl methacrylates) in the presence of CPDB (since the thiophene-based RAFT agents showed unfavorable rate retardation) in different solvents, namely: toluene, 2-propanol and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) at different temperatures, namely: 60, 30, 4, and -18 °C. The prepared polymers were characterized by 1 H-NMR spectroscopy in order to monitor the tacticity and SEC for the determination of the controlled/living behavior of the polymerization system. Results showed that the simultaneous control of the molecular weight and stereochemistry of PMMA was accomplished via RAFT-mediated polymerization, especially in HFIP at -18 °C, where the syndiotactic content of the polymer was the· highest and low PDI values (< 1.4) were achieved.